 FM Wave Circuit Modulator

Objective

• To build an FM wave circuit using discrete and / or integrated circuits

Discussion

Frequency Modulation- defined

Frequency Modulation differs from amplitude modulation in many ways. Instead of varying the amplitude of the peak of the RF signal in proportion to the amplitude of the modulating signal, in FM the amplitude of the peak is held constant.

The amplitude of the modulating of the modulating signal is represented by the amount of frequency deviation of the RF from the center (rest,carrier) frequency. The frequency of the modulating signal is represented by the rate of the deviation of the carrier frequency.

Circuit Components and Operation

566 IC

Theory of Operation and Circuit Parameters

The 566 contains current sources to charge and discharge an external capacitor at a rate set by external resistor and the modulating dc input voltage. A schmitt trigger circuit is used to switch the current sources between charging and discharging the capacitor, and triangular voltage developed across the capacitor

The FM Circuit shows an example I which the 566 function generator is used to provide both square wave triangular wave signals at a fixed frequency set by the resistor and capacitor.

List of Components

Semiconductor

IC1 566

Resistors (All are 0.5W, 5% tolerance. Unless otherwise specified.)

2 10 K

1 1.5 K

Capacitor

1 220 pF

Conclusion

In this circuit construction, we were able to find the following conclusions and generalizations:

• FM-Wave circuits can be made by two different techniques, using discrete and / or integrated components.
• Proper biasing is important to achieve the desired signal output.
• The output signal is fairly attenuated when using the UHF range of frequencies.

• The existence of modulating integrated circuits allows the simplification of discrete modulation circuits.
• The 566 Voltage – Controlled Oscillator IC cannot exceed 1MHz as its center frequency